Twenty-five species belonging to 12 families were studied. Their habitats ranged from coastal, pelagic zones to depths of about 300 meters. Corresponding variations in retinal structure, intraocular circulation, and activity were observed. Based on these, three categories have been established. The first includes species with poorly developed retinae, very sparse circulation, and no activity, inhabiting deeper waters; the third comprises active species with well-developed retinae and good blood supply, inhabiting coastal or pelagic zones. The second category groups the intermediate forms. Variations in retinal structure and circulation and the relationship between the two aspects are discussed.
The characteristic feature of the retina of Lepidosiren paradoxa is the hugeness (20–25 μm) and sparse-ness of the cells which compose it. The epithelial layer is well pigmented. The visual cells may be classified into rods and single cones which possess a large oil droplet and a smaller paraboloid. Neither the epithelial pigment nor the visual cells show retinomotor responses. Landolt's clubs arising from the bipolar cells and terminating amidst the epithelial cell processes are present and resemble those of another Dipnoan, Protopterus. The ratio of photoreceptor, bipolar, and ganglion cells is about 2:2:1, indicating a very low degree of summation. There is no noticeable difference among the dorsal, vental, temporal, and nasal regions of the retina. The similarity of this retina to that of other dipnoans and urodeles is briefly discussed. It appears as if the growth of the eye were arrested (neoteny) during the evolution of this genus because of the insignificant role of vision in its life.
Abstract The effects of monoamines and adrenergic drugs on luminescent responses and rachidial contractions were investigated in the colony of the sea pansy Renilla köllikeri . Of several transmitter candidates tested, only adrenaline induced localized, phasic luminescence at low concentrations. Propranolol (1 mM) depressed adrenaline‐induced and suppressed electrically stimulated luminescence, the latter being also abolished by 6‐hydroxydopamine (6‐OHDA) and reserpine. Desmethylimipramine (DMI, 20 μM), an uptake inhibitor of adrenergic neurons, potentiated luminescent responses to both adrenaline and electrical stimulation, and induced luminescence at higher concentrations. Pargyline, a monoamine oxidase inhibitor, produced DMI‐like effects. Rachidial contractions in Renilla are biphasic events which are usually spontaneous and rhythmic, or can be induced by electrical stimulation. Noradrenaline and adrenaline enhanced the second phase of ongoing rhythmic contractions, but failed to induce contractions. Reserpine and 6‐OHDA abolished electrically stimulated luminescence, but reserpine further depressed evoked contractions while 6‐OHDA failed to affect rhythmic or evoked contractions. DMI (0.5 mM) initiated rhythmic contractile activity in quiescent preparations. These observations suggest that adrenaline or an as yet unidentified catecholamine may be involved as a neurotransmitter in luminescence control. Noradrenaline and/or adrenaline act possibly as neuromodulators for rachidial contractions in the sea pansy.
Abstract. Although peptides similar to gonadotropin‐releasing hormone (GnRH) peptides have been reported in various taxa of invertebrates, no such evidence has yet been identified for platyhelminths. Antibodies raised against mammalian GnRH were used to investigate the distribution of GnRH immunoreactivity in specimens of the triclad turbellarian Bdelloura candida (Maricola, Bdellouridae). While no GnRH immunoreactivity was detected in the brain and nerve cords, both the putative subepidermal and submuscular nerve plexuses appeared to be immunoreactive. GnRH immunoreactivity was also present in epidermal mucous cells, in parenchymal cells, including cells surrounding the branches of the intestine, in putative neuroendocrine cells associated with the testes, and in the vitellogenic gland cells associated with the oviduct. These observations suggest that the GnRH‐like material found in specimens of B. candida may be involved in a variety of functions, including a possible pheromone‐like role for mucous cells and the control of specific reproductive activities.
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